Another Mark Keppinger Theremin is Born

Well after a little more than a year of off-an-on progress I finally finished it and I m very pleased with the result. I posted a photo album of the finished

Message 1 of 9
, Mar 1 6:17 PM

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Well after a little more than a year of off-an-on progress I finally finished it and I'm very pleased with the result. I posted a photo album of the finished Theremin in this group's Photos folder. I believe this chassis set is the last of the original batch from Mark by way of Kyle. For the group's reference, I posted two documents with chassis dimensions in this group's Files folder.

I would like to thank Mark and Kyle for their generous guidance early on and to Phillip for making his very helpful experience available on his website. I followed the J. Sparks schematics (Rev 7  dated 12/20/2008) closely and made no electronic changes. I'm very happy to report that it worked very well from the moment I first plugged it in. No problems with the oscillators (knock on wood), they seem rock solid. It sings beautifully. The wave forms are clean and display similar to those on Phillip's website.

I did incorporate a few parts and layout enhancements partly based on comments of previous builders:

It was commented that the 3K resistor in the power supply can get hot so I installed a 50 watt with heat-sink mounted to the chassis. As you might guess, it runs very cool. In fact all the components run very cool (except the tubes of course).

To make the oscillator trimmers more accessible, I mounted them upside-down on the terminal strip and drilled holes through the top of the chassis to make the adjustment. I inserted a grommet in each hole to help guide the non-metallic screwdriver to the adjustment screw. It works quite well.

In the pitch and tone oscillators, I installed a 500pf capacitor in each for Concert Tuning (that was as close to 430pf as I had). I then piggy backed each capacitor with an additional a 200pf in the pitch oscillator and a 250pf in the tone oscillator. Now I can easily experiment back and forth from Concert to Bass by just taking the piggy packed caps in and out of circuit.

I crafted and applied decal labels to both chassis' to identify the controls and tubes. I also included a decal indicating its a Mark Keppinger design.

Until I have a cabinet constructed, the chassis's will be open and exposed. To keep small grandchildren's hands out of bad places, I made black perforated aluminum covers that completely cover the bottom and sides of each chassis. The pattern of 3/16" perforations on 1/4" centers allow more than sufficient ventilation. The covers aren't shown in the photos.

The wiring is cloth reproduction wire from Radio Daze. The chassis's are painted with Hammer-tone Copper.

Part of the delay in getting the build done was first making a coil winder (reference photo in the gallery). I used a motor drive using a motor with a gear reduction to 20 rpm and providing sufficient torque (purchased on Antique Radio Forums). I utilized an inexpensive belt and pulleys (available on Amazon) to have the ability to adjust the speed if needed. I use a digital counter I found on Ebay. The coil winder and motor drive worked very well and efficiently  I was able to wind all the coils in just a couple hours.

My next project is to make the antennas. I currently have a Mickey Mouse version that I fashioned from 14 gauge electrical ground wire. It works for the moment. I have read various posts regarding making a reproduction RCA antenna  If anyone has a relatively easy approach to this or pitfalls I should avoid please let me know.

I will also tackle making a cabinet. I'm considering incorporating a 10" speaker but also trying to keep the design suggestive of the RCA Theremin  not sure yet how to accomplish both.

Guidance needed: I need some perspectives in adjusting the various trimmers, etc. I've found they interact enough that I'm not sure if any of my adjustments are optimal or that I'm converging on the most accurate overall adjustment. I would appreciate any insights  ideally if you have a tried and true procedure to methodically or iteratively accomplish this please let me know. Also what tests or symptoms have you found that indicate misalignment?

Regards,

Richard Watts

mkepp@hevanet.com

Richard; Congrats on a job well done! You have joined the elite although growing group of those who have completed a Theremin based on my design. Back when I

Message 2 of 9
, Mar 1 9:41 PM

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Richard;

Congrats on a job well done! You have joined the elite although growing
group of those who have completed a Theremin based on my design. Back
when I made my schematic public domain, I figured that one or two people
might attempt this undertaking and then eventually give up. I never
dreamed that not only would there be this many success stories, but that
those who embarked on this path would share their experiences and help
others that followed them. How cool is that!?

I don't think that there is going to be a perfect set of oscillator
frequencies that works for everyone in all locations; mostly because AM
radio transmitters are going to hetrodyne with the oscillators and
produce "birdies" (unwanted byproducts of RF signals mixing).
Experimenting with the tuning is truly your best bet. When you find
something that works for you, document it if possible, and you can always
go back to it at a later time.

Mark Keppinger

> Well after a little more than a year of off-an-on progress I finally
> finished it and I'm very pleased with the result. I posted a photo
> album of the finished Theremin in this group's Photos folder. I
> believe this chassis set is the last of the original batch from Mark by
> way of Kyle. For the group's reference, I posted two documents with
> chassis dimensions in this group's Files folder.
>
> I would like to thank Mark and Kyle for their generous guidance early on
> and to Phillip for making his very helpful experience available on his
> website. I followed the J. Sparks schematics (Rev 7 � dated
> 12/20/2008) closely and made no electronic changes. I'm very happy
> to report that it worked very well from the moment I first plugged it
> in. No problems with the oscillators (knock on wood), they seem rock
> solid. It sings beautifully. The wave forms are clean and display
> similar to those on Phillip's website.
>
> I did incorporate a few parts and layout enhancements partly based on
> comments of previous builders:
> It was commented that the 3K resistor in the power supply can get hot so
> I installed a 50 watt with heat-sink mounted to the chassis. As you
> might guess, it runs very cool. In fact all the components run very
> cool (except the tubes of course).
>
> To make the oscillator trimmers more accessible, I mounted them
> upside-down on the terminal strip and drilled holes through the top of
> the chassis to make the adjustment. I inserted a grommet in each hole
> to help guide the non-metallic screwdriver to the adjustment screw. It
> works quite well.
>
> In the pitch and tone oscillators, I installed a 500pf capacitor in each
> for Concert Tuning (that was as close to 430pf as I had). I then piggy
> backed each capacitor with an additional a 200pf in the pitch oscillator
> and a 250pf in the tone oscillator. Now I can easily experiment back
> and forth from Concert to Bass by just taking the piggy packed caps in
> and out of circuit.
>
> I crafted and applied decal labels to both chassis' to identify the
> controls and tubes. I also included a decal indicating its a Mark
> Keppinger design.
>
> Until I have a cabinet constructed, the chassis's will be open and
> exposed. To keep small grandchildren's hands out of bad places, I made
> black perforated aluminum covers that completely cover the bottom and
> sides of each chassis. The pattern of 3/16" perforations on 1/4"
> centers allow more than sufficient ventilation. The covers aren't shown
> in the photos.
>
> The wiring is cloth reproduction wire from Radio Daze. The chassis's
> are painted with Hammer-tone Copper.
> Part of the delay in getting the build done was first making a coil
> winder (reference photo in the gallery). I used a motor drive using a
> motor with a gear reduction to 20 rpm and providing sufficient torque
> (purchased on Antique Radio Forums). I utilized an inexpensive belt and
> pulleys (available on Amazon) to have the ability to adjust the speed if
> needed. I use a digital counter I found on Ebay. The coil winder and
> motor drive worked very well and efficiently � I was able to wind
> all the coils in just a couple hours.
>
> My next project is to make the antennas. I currently have a Mickey
> Mouse version that I fashioned from 14 gauge electrical ground wire. It
> works for the moment. I have read various posts regarding making a
> reproduction RCA antenna � If anyone has a relatively easy approach
> to this or pitfalls I should avoid please let me know.
>
> I will also tackle making a cabinet. I'm considering incorporating
> a 10" speaker but also trying to keep the design suggestive of the
> RCA Theremin � not sure yet how to accomplish both.
>
> Guidance needed: I need some perspectives in adjusting the various
> trimmers, etc. I've found they interact enough that I'm not
> sure if any of my adjustments are optimal or that I'm converging on
> the most accurate overall adjustment. I would appreciate any insights
> � ideally if you have a tried and true procedure to methodically or
> iteratively accomplish this please let me know. Also what tests or
> symptoms have you found that indicate misalignment?
>
> Regards,
>
> Richard Watts
>
>

Jean Lucas

Hi Richard, Congratulations for your work! The wiring looks perfect, and your coil winder seems great too ! I have a question about the octal plug you use : I

I have a question about the octal plug you use : I was planning to use a tube base for my (future) Keppinger Theremin building, but it's not very satisfactory because it's open. On the contrary, your plug is closed. Did you build it from a "standart" tube base or did you find another kind of octal plug ? If yes, could you tell me where ?

Well after a little more than a year of off-an-on progress I finally finished it and I'm very pleased with the result. I posted a photo album of the finished Theremin in this group's Photos folder. I believe this chassis set is the last of the original batch from Mark by way of Kyle. For the group's reference, I posted two documents with chassis dimensions in this group's Files folder.

I would like to thank Mark and Kyle for their generous guidance early on and to Phillip for making his very helpful experience available on his website. I followed the J. Sparks schematics (Rev 7 – dated 12/20/2008) closely and made no electronic changes. I'm very happy to report that it worked very well from the moment I first plugged it in. No problems with the oscillators (knock on wood), they seem rock solid. It sings beautifully. The wave forms are clean and display similar to those
on Phillip's website.

I did incorporate a few parts and layout enhancements partly based on comments of previous builders:

It was commented that the 3K resistor in the power supply can get hot so I installed a 50 watt with heat-sink mounted to the chassis. As you might guess, it runs very cool. In fact all the components run very cool (except the tubes of course).

To make the oscillator trimmers more accessible, I mounted them upside-down on the terminal strip and drilled holes through the top of the chassis to make the adjustment. I inserted a grommet in each hole to help guide the non-metallic screwdriver to the adjustment screw. It works quite well.

In the pitch and tone oscillators, I installed a 500pf capacitor in each for Concert Tuning (that was as close to 430pf as I had). I then
piggy backed each capacitor with an additional a 200pf in the pitch oscillator and a 250pf in the tone oscillator. Now I can easily experiment back and forth from Concert to Bass by just taking the piggy packed caps in and out of circuit.

I crafted and applied decal labels to both chassis' to identify the controls and tubes. I also included a decal indicating its a Mark Keppinger design.

Until I have a cabinet constructed, the chassis's will be open and exposed. To keep small grandchildren's hands out of bad places, I made black perforated aluminum covers that completely cover the bottom and sides of each chassis. The pattern of 3/16" perforations on 1/4" centers allow more than sufficient ventilation. The covers aren't shown in the photos.

The wiring is cloth reproduction wire from Radio Daze. The chassis's are painted with Hammer-tone
Copper.

Part of the delay in getting the build done was first making a coil winder (reference photo in the gallery). I used a motor drive using a motor with a gear reduction to 20 rpm and providing sufficient torque (purchased on Antique Radio Forums). I utilized an inexpensive belt and pulleys (available on Amazon) to have the ability to adjust the speed if needed. I use a digital counter I found on Ebay. The coil winder and motor drive worked very well and efficiently – I was able to wind all the coils in just a couple hours.

My next project is to make the antennas. I currently have a Mickey Mouse version that I fashioned from 14 gauge electrical ground wire. It works for the moment. I have read various posts regarding making a reproduction RCA antenna – If anyone has a relatively easy approach to this or pitfalls I should avoid please let me know.

I will also tackle making a cabinet. I'm considering incorporating a 10" speaker but also trying to keep the design suggestive of the RCA Theremin – not sure yet how to accomplish both.

Guidance needed: I need some perspectives in adjusting the various trimmers, etc. I've found they interact enough that I'm not sure if any of my adjustments are optimal or that I'm converging on the most accurate overall adjustment. I would appreciate any insights – ideally if you have a tried and true procedure to methodically or iteratively accomplish this please let me know. Also what tests or symptoms have you found that indicate misalignment?

Regards,

Richard Watts

Richard Watts

Mark and Jean, thank you for the kind words. Jean the octal plug is vintage 1940s/50s and is made with a groove around the circumference to hold the snap on

Message 4 of 9
, Mar 2 11:31 AM

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Mark and Jean, thank you for the kind words.

Jean the octal plug is vintage 1940s/50s and is made with a groove around the circumference to hold the snap on cap. The cap didn’t have a hole for the cable so I had to drill it and insert a grommet. I found the plug and cap at a radio club swap meet for $1.

I have a question about the octal plug you use : I was planning to use a tube base for my (future) Keppinger Theremin building, but it's not very satisfactory because it's open. On the contrary, your plug is closed. Did you build it from a "standart" tube base or did you find another kind of octal plug ? If yes, could you tell me where ?

Well after a little more than a year of off-an-on progress I finally finished it and I'm very pleased with the result. I posted a photo album of the finished Theremin in this group's Photos folder. I believe this chassis set is the last of the original batch from Mark by way of Kyle. For the group's reference, I posted two documents with chassis dimensions in this group's Files folder.

I would like to thank Mark and Kyle for their generous guidance early on and to Phillip for making his very helpful experience available on his website. I followed the J. Sparks schematics (Rev 7 – dated 12/20/2008) closely and made no electronic changes. I'm very happy to report that it worked very well from the moment I first plugged it in. No problems with the oscillators (knock on wood), they seem rock solid. It sings beautifully. The wave forms are clean and display similar to those on Phillip's website.

I did incorporate a few parts and layout enhancements partly based on comments of previous builders:

It was commented that the 3K resistor in the power supply can get hot so I installed a 50 watt with heat-sink mounted to the chassis. As you might guess, it runs very cool. In fact all the components run very cool (except the tubes of course).

To make the oscillator trimmers more accessible, I mounted them upside-down on the terminal strip and drilled holes through the top of the chassis to make the adjustment. I inserted a grommet in each hole to help guide the non-metallic screwdriver to the adjustment screw. It works quite well.

In the pitch and tone oscillators, I installed a 500pf capacitor in each for Concert Tuning (that was as close to 430pf as I had). I then piggy backed each capacitor with an additional a 200pf in the pitch oscillator and a 250pf in the tone oscillator. Now I can easily experiment back and forth from Concert to Bass by just taking the piggy packed caps in and out of circuit.

I crafted and applied decal labels to both chassis' to identify the controls and tubes. I also included a decal indicating its a Mark Keppinger design.

Until I have a cabinet constructed, the chassis's will be open and exposed. To keep small grandchildren's hands out of bad places, I made black perforated aluminum covers that completely cover the bottom and sides of each chassis. The pattern of 3/16" perforations on 1/4" centers allow more than sufficient ventilation. The covers aren't shown in the photos.

The wiring is cloth reproduction wire from Radio Daze. The chassis's are painted with Hammer-tone Copper.

Part of the delay in getting the build done was first making a coil winder (reference photo in the gallery). I used a motor drive using a motor with a gear reduction to 20 rpm and providing sufficient torque (purchased on Antique Radio Forums). I utilized an inexpensive belt and pulleys (available on Amazon) to have the ability to adjust the speed if needed. I use a digital counter I found on Ebay. The coil winder and motor drive worked very well and efficiently – I was able to wind all the coils in just a couple hours.

My next project is to make the antennas. I currently have a Mickey Mouse version that I fashioned from 14 gauge electrical ground wire. It works for the moment. I have read various posts regarding making a reproduction RCA antenna – If anyone has a relatively easy approach to this or pitfalls I should avoid please let me know.

I will also tackle making a cabinet. I'm considering incorporating a 10" speaker but also trying to keep the design suggestive of the RCA Theremin – not sure yet how to accomplish both.

Guidance needed: I need some perspectives in adjusting the various trimmers, etc. I've found they interact enough that I'm not sure if any of my adjustments are optimal or that I'm converging on the most accurate overall adjustment. I would appreciate any insights – ideally if you have a tried and true procedure to methodically or iteratively accomplish this please let me know. Also what tests or symptoms have you found that indicate misalignment?

Regards,

Richard Watts

Jean Lucas

Richard, thanks for your answer. Concerning the antennas, you may know that Mike Buffington has built several RCA reproduction antenna sets, as you can see

Jean the octal plug is vintage 1940s/50s and is made with a groove around the circumference to hold the snap on cap. The cap didn’t have a hole for the cable so I had to drill it and insert a grommet. I found the plug and cap at a radio club swap meet for $1.

I have a question about the octal plug you use : I was planning to use a tube base for my (future) Keppinger Theremin building, but it's not very
satisfactory because it's open. On the contrary, your plug is closed. Did you build it from a "standart" tube base or did you find another kind of octal plug ? If yes, could you tell me where ?

Well after a little
more than a year of off-an-on progress I finally finished it and I'm very pleased with the result. I posted a photo album of the finished Theremin in this group's Photos folder. I believe this chassis set is the last of the original batch from Mark by way of Kyle. For the group's reference, I posted two documents with chassis dimensions in this group's Files folder.

I would like to thank Mark and Kyle for their generous guidance early on and to Phillip for making his very helpful experience available on his website. I followed the J. Sparks schematics (Rev 7 – dated 12/20/2008) closely and made no electronic changes. I'm very happy to report that it worked very well from the moment I first plugged it in. No problems with the oscillators (knock on wood), they seem rock solid. It sings beautifully. The wave forms are clean and display similar to those on Phillip's website.

I did
incorporate a few parts and layout enhancements partly based on comments of previous builders:

It was commented that the 3K resistor in the power supply can get hot so I installed a 50 watt with heat-sink mounted to the chassis. As you might guess, it runs very cool. In fact all the components run very cool (except the tubes of course).

To make the oscillator trimmers more accessible, I mounted them upside-down on the terminal strip and drilled holes through the top of the chassis to make the adjustment. I inserted a grommet in each hole to help guide the non-metallic screwdriver to the adjustment screw. It works quite well.

In the pitch and tone oscillators, I installed a 500pf capacitor in each for Concert Tuning (that was as close to 430pf as I had). I then piggy backed each capacitor with an additional a 200pf in the
pitch oscillator and a 250pf in the tone oscillator. Now I can easily experiment back and forth from Concert to Bass by just taking the piggy packed caps in and out of circuit.

I crafted and applied decal labels to both chassis' to identify the controls and tubes. I also included a decal indicating its a Mark Keppinger design.

Until I have a cabinet constructed, the chassis's will be open and exposed. To keep small grandchildren's hands out of bad places, I made black perforated aluminum covers that completely cover the bottom and sides of each chassis. The pattern of 3/16" perforations on 1/4" centers allow more than sufficient ventilation. The covers aren't shown in the photos.

The wiring is cloth reproduction wire from Radio Daze. The chassis's are painted with Hammer-tone Copper.

Part of the delay in getting the build done was
first making a coil winder (reference photo in the gallery). I used a motor drive using a motor with a gear reduction to 20 rpm and providing sufficient torque (purchased on Antique Radio Forums). I utilized an inexpensive belt and pulleys (available on Amazon) to have the ability to adjust the speed if needed. I use a digital counter I found on Ebay. The coil winder and motor drive worked very well and efficiently – I was able to wind all the coils in just a couple hours.

My next project is to make the antennas. I currently have a Mickey Mouse version that I fashioned from 14 gauge electrical ground wire. It works for the moment. I have read various posts regarding making a reproduction RCA antenna – If anyone has a relatively easy approach to this or pitfalls I should avoid please let me know.

I will also tackle making a cabinet. I'm considering incorporating a 10" speaker
but also trying to keep the design suggestive of the RCA Theremin – not sure yet how to accomplish both.

Guidance needed: I need some perspectives in adjusting the various trimmers, etc. I've found they interact enough that I'm not sure if any of my adjustments are optimal or that I'm converging on the most accurate overall adjustment. I would appreciate any insights – ideally if you have a tried and true procedure to methodically or iteratively accomplish this please let me know. Also what tests or symptoms have you found that indicate misalignment?

Regards,

Richard Watts

Mark Keppinger

Jean; I would recommend solid (not tubing) brass. 1/4 can be formed by hand for the volume loop, but 3/8 is going to be fairly difficult. I did try making a

Message 6 of 9
, Mar 3 8:01 AM

0 Attachment

﻿

Jean;

I would recommend solid (not tubing) brass. 1/4"
can be formed by hand for the volume loop, but 3/8" is going to be fairly
difficult. I did try making a 'bending jig', but the one that gave me the shape
I wanted also scarred the metal, which is why I went ahead and bent them by
hand, which wasn't as easy as it sounds.

Jean the octal
plug is vintage 1940s/50s and is made with a groove around the circumference
to hold the snap on cap. The cap didn’t have a hole for the cable so I
had to drill it and insert a grommet. I found the plug and cap at a
radio club swap meet for $1.

I have a
question about the octal plug you use : I was planning to use a tube base for
my (future) Keppinger Theremin building, but it's not very satisfactory
because it's open. On the contrary, your plug is closed. Did you build it from
a "standart" tube base or did you find another kind of octal plug ? If yes,
could you tell me where ?

Well after a little more than a year of off-an-on progress I finally
finished it and I'm very pleased with the result. I posted a photo album
of the finished Theremin in this group's Photos folder. I believe this
chassis set is the last of the original batch from Mark by way of Kyle.
For the group's reference, I posted two documents with chassis dimensions in
this group's Files folder.

I would like to thank Mark and Kyle for
their generous guidance early on and to Phillip for making his very helpful
experience available on his website. I followed the J. Sparks schematics
(Rev 7 – dated 12/20/2008) closely and made no electronic changes. I'm
very happy to report that it worked very well from the moment I first plugged
it in. No problems with the oscillators (knock on wood), they seem rock
solid. It sings beautifully. The wave forms are clean and display
similar to those on Phillip's website.

I did incorporate a few
parts and layout enhancements partly based on comments of previous
builders:

It was commented that the 3K resistor in the power
supply can get hot so I installed a 50 watt with heat-sink mounted to the
chassis. As you might guess, it runs very cool. In fact all the
components run very cool (except the tubes of
course).

To make the oscillator trimmers more
accessible, I mounted them upside-down on the terminal strip and drilled
holes through the top of the chassis to make the adjustment. I
inserted a grommet in each hole to help guide the non-metallic screwdriver
to the adjustment screw. It works quite well.

In the pitch and tone oscillators, I installed a
500pf capacitor in each for Concert Tuning (that was as close to 430pf as I
had). I then piggy backed each capacitor with an additional a 200pf in
the pitch oscillator and a 250pf in the tone oscillator. Now I can
easily experiment back and forth from Concert to Bass by just taking the
piggy packed caps in and out of circuit.

I crafted and
applied decal labels to both chassis' to identify the controls and
tubes. I also included a decal indicating its a Mark Keppinger
design.

Until I have a cabinet constructed, the chassis's will be
open and exposed. To keep small grandchildren's hands out of bad
places, I made black perforated aluminum covers that completely cover the
bottom and sides of each chassis. The pattern of 3/16" perforations on
1/4" centers allow more than sufficient ventilation. The covers aren't
shown in the photos.

The wiring is cloth reproduction wire from
Radio Daze. The chassis's are painted with Hammer-tone
Copper.

Part of the delay in getting the build done was first
making a coil winder (reference photo in the gallery). I used a motor
drive using a motor with a gear reduction to 20 rpm and providing sufficient
torque (purchased on Antique Radio Forums). I utilized an inexpensive
belt and pulleys (available on Amazon) to have the ability to adjust the speed
if needed. I use a digital counter I found on Ebay. The coil
winder and motor drive worked very well and efficiently – I was able to wind
all the coils in just a couple hours.

My next project is to make
the antennas. I currently have a Mickey Mouse version that I fashioned
from 14 gauge electrical ground wire. It works for the moment. I
have read various posts regarding making a reproduction RCA antenna – If
anyone has a relatively easy approach to this or pitfalls I should avoid
please let me know.

I will also tackle making a cabinet.
I'm considering incorporating a 10" speaker but also trying to keep the design
suggestive of the RCA Theremin – not sure yet how to accomplish
both.

Guidance needed: I need some perspectives in
adjusting the various trimmers, etc. I've found they interact enough
that I'm not sure if any of my adjustments are optimal or that I'm converging
on the most accurate overall adjustment. I would appreciate any insights
– ideally if you have a tried and true procedure to methodically or
iteratively accomplish this please let me know. Also what tests or
symptoms have you found that indicate misalignment?

Mark, infact, I was planning to use 8mm solid copper (rather than brass), because I know someone who can give me the necessary length of it. Moreover, copper

Message 7 of 9
, Mar 3 12:01 PM

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Mark,

infact, I was planning to use 8mm solid copper (rather than brass), because I know someone who can give me the necessary length of it. Moreover, copper should be easier to work with and conducts electricity better (this difference may not be so important in this very case). I was thinking to something similar to what can be seen on Mike Buffington's page to bend the rod. heating it should make the things easier too I think.

I'll then try to find someone who can electro-plate the antennas. Nickel should be right.

By the way, I'm a student in science and I have chosen the theremin as a subject for my oral examination at the end of the year. I'll focus on how the wave is produed, heterodyne and so forth... I use your schematic as the main source.

I would recommend solid (not tubing) brass. 1/4"
can be formed by hand for the volume loop, but 3/8" is going to be fairly
difficult. I did try making a 'bending jig', but the one that gave me the shape
I wanted also scarred the metal, which is why I went ahead and bent them by
hand, which wasn't as easy as it sounds.

Jean the octal
plug is vintage 1940s/50s and is made with a groove around the circumference
to hold the snap on cap. The cap didn’t have a hole for the cable so I
had to drill it and insert a grommet. I found the plug and cap at a
radio club swap meet for $1.

I have a
question about the octal plug you use : I was planning to use a tube base for
my (future) Keppinger Theremin building, but it's not very satisfactory
because it's open. On the contrary, your plug is closed. Did you build it from
a "standart" tube base or did you find another kind of octal plug ? If yes,
could you tell me where ?

Well after a little more than a year of off-an-on progress I finally
finished it and I'm very pleased with the result. I posted a photo album
of the finished Theremin in this group's Photos folder. I believe this
chassis set is the last of the original batch from Mark by way of Kyle.
For the group's reference, I posted two documents with chassis dimensions in
this group's Files folder.

I would like to thank Mark and Kyle for
their generous guidance early on and to Phillip for making his very helpful
experience available on his website. I followed the J. Sparks schematics
(Rev 7 – dated 12/20/2008) closely and made no electronic changes. I'm
very happy to report that it worked very well from the moment I first plugged
it in. No problems with the oscillators (knock on wood), they seem rock
solid. It sings beautifully. The wave forms are clean and display
similar to those on Phillip's website.

I did incorporate a few
parts and layout enhancements partly based on comments of previous
builders:

It was commented that the 3K resistor in the power
supply can get hot so I installed a 50 watt with heat-sink mounted to the
chassis. As you might guess, it runs very cool. In fact all the
components run very cool (except the tubes of
course).

To make the oscillator trimmers more
accessible, I mounted them upside-down on the terminal strip and drilled
holes through the top of the chassis to make the adjustment. I
inserted a grommet in each hole to help guide the non-metallic screwdriver
to the adjustment screw. It works quite well.

In the pitch and tone oscillators, I installed a
500pf capacitor in each for Concert Tuning (that was as close to 430pf as I
had). I then piggy backed each capacitor with an additional a 200pf in
the pitch oscillator and a 250pf in the tone oscillator. Now I can
easily experiment back and forth from Concert to Bass by just taking the
piggy packed caps in and out of circuit.

I crafted and
applied decal labels to both chassis' to identify the controls and
tubes. I also included a decal indicating its a Mark Keppinger
design.

Until I have a cabinet constructed, the chassis's will be
open and exposed. To keep small grandchildren's hands out of bad
places, I made black perforated aluminum covers that completely cover the
bottom and sides of each chassis. The pattern of 3/16" perforations on
1/4" centers allow more than sufficient ventilation. The covers aren't
shown in the photos.

The wiring is cloth reproduction wire from
Radio Daze. The chassis's are painted with Hammer-tone
Copper.

Part of the delay in getting the build done was first
making a coil winder (reference photo in the gallery). I used a motor
drive using a motor with a gear reduction to 20 rpm and providing sufficient
torque (purchased on Antique Radio Forums). I utilized an inexpensive
belt and pulleys (available on Amazon) to have the ability to adjust the speed
if needed. I use a digital counter I found on Ebay. The coil
winder and motor drive worked very well and efficiently – I was able to wind
all the coils in just a couple hours.

My next project is to make
the antennas. I currently have a Mickey Mouse version that I fashioned
from 14 gauge electrical ground wire. It works for the moment. I
have read various posts regarding making a reproduction RCA antenna – If
anyone has a relatively easy approach to this or pitfalls I should avoid
please let me know.

I will also tackle making a cabinet.
I'm considering incorporating a 10" speaker but also trying to keep the design
suggestive of the RCA Theremin – not sure yet how to accomplish
both.

Guidance needed: I need some perspectives in
adjusting the various trimmers, etc. I've found they interact enough
that I'm not sure if any of my adjustments are optimal or that I'm converging
on the most accurate overall adjustment. I would appreciate any insights
– ideally if you have a tried and true procedure to methodically or
iteratively accomplish this please let me know. Also what tests or
symptoms have you found that indicate misalignment?

Jean; The conductivity will make no difference whatsoever. I *think* that brass is easier to nickel plate than copper. As I recall, it takes one more step

Message 8 of 9
, Mar 3 12:04 PM

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Jean;

The conductivity will make no difference whatsoever. I *think* that brass
is easier to nickel plate than copper. As I recall, it takes one more
step (using something called "q-posite?) in the process. The only
diffence between nickel and chrome plating is an added step at the end
which applies the chrome (which is clear) plating over the nickel,
keeping it from tarnishing.

Good luck with your class project!

Mark

> Mark,
>
> infact, I was planning to use 8mm solid copper (rather than brass),

because> I

> know someone who can give me the necessary length of it. Moreover,

copper
s> hould

> be easier to work with and conducts electricity better (this difference

may> not

> be so important in this very case). I was thinking to something similar

to

> what
> can be seen on Mike Buffington's page to bend the rod. heating it should

ma> ke

> the things easier too I think.
>
> I'll then try to find someone who can electro-plate the antennas. Nickel

sh> ould

> be right.
>
> By the way, I'm a student in science and I have chosen the theremin as a

su> bject

> for my oral examination at the end of the year. I'll focus on how the

wave

> is
> produed, heterodyne and so forth... I use your schematic as the main